Not using Tailscale but knocked up a VPN between my various servers to allow e.g. my tiny mail frontend to use the extremely heavy ClamAV on my big mail backend

Not using Tailscale but knocked up a VPN between my various servers to allow e.g. my tiny mail frontend to use the extremely heavy ClamAV on my big mail backend without having to expose it to the wider internet. Same with allowing all the servers access to each others' Redis's for synchronisation of things like rspamd whitelists (easier than setting up Redis replication, for me.)